An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

This apartment is a true time capsule of local life in Bulgaria during the Soviet regime.

This small chapel is built of human bones and decorated with a golden skeleton.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

The tragedy of the Japanese internment camps is remembered here by a stark "Soul Consoling Tower."

This monument remembers the first Japanese Americans forcibly relocated during World War II.

A museum in rural Utah documents the history of the Japanese Americans who were forcibly relocated there.

A Jenga-style cylindrical tower of books that appears to go on forever.

Now abandoned, the first public health hospital in the U.S. saw more than one million immigrants from around the world.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.

Since the 1960s, this small village has invited painters to decorate its walls.

The grotto where Saint Ignatius of Loyola lived as a hermit for nearly a year.

This Central New York ghost town was once a prosperous railroad community.

This 19th-century pub features stained-glass windows celebrating Victorian-era "champions."

This unassuming retro burger joint was billed as “diner of the future” at the 1939 World's Fair.

A rare example of World War I trenches from the British front.

The absurd creation is a compulsory destination for selfies in Buffalo.

Concerts, art, offices, and a café in what used to be Berlin's first crematorium.

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

This uniquely designed bridge served as the city gate for Comacchio.

This platform is now a memorial dedicated to those who were deported during the Holocaust.

A 115-year-old restored German dining hall awaits those who venture beneath the Minnesota State Capitol.